Recently, a vacuum die casting apparatus, which forms production by providing a molten metal such as aluminum (Al) to a mold, is widely used in a state that a pressure in a cavity is reduced by a vacuum pump. The cavity is formed surrounding the mold. A conventional technology with respect to the vacuum die casting is, for example, disclosed in Japanese Unexamined Patent Application Publication No. 64-87051. Die casting using the vacuum die casting apparatus allows the molten metal to flow well during injection and prevents defects due to air. Therefore, casting defects such as blowholes may be reduced.
For a die casting using the vacuum die casting apparatus, before injecting the molten metal, a powder release agent is applied to the inside surface of the cavity to release the cast product from the mold smoothly. Therefore, when gas in the cavity is sucked by the vacuum pump, there is a problem that the vacuum pump sucks residue of the powder release agent and the vacuum pump is damaged due to the residue. A mesh size of a filter which is disposed between the mold and the vacuum pump has been made small to improve the above-described problem. However, a new issue occurred that the filter became clogged quickly and production efficiency was decreased.
Therefore, in common vacuum die casting apparatuses in use, casting has been performed by using the vacuum pump having relatively low pressure reducing capacity without reducing the mesh size of the filter much. A vacuum pump having relatively low pressure reducing capacity is difficult to damage even if the powder release agent enters the pump. Therefore, in common vacuum die casting apparatuses, it was difficult to reduce the casting defects of the cast product and a vacuum degree in the cavity was not so high. Also, in common vacuum die casting apparatuses, it was difficult to improve productivity and it took time to reach the vacuum degree in the cavity to a target value.